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Plug-in hybrid electric vehicles (PHEVs) with post-transmission parallel configuration attracted considerable attention due to their capacity to operate in either electric vehicle (EV) mode or hybrid electric vehicle (HEV) mode. Meanwhile, the added flexibility and multiple operation modes add additional challenges to vehicle control with acceptable drivability, particularly during the mode transition from the EV and HEV, since proper control is needed for the internal combustion engine (ICE), motor and coupling device to achieve smooth and fast transition, under various vehicle operation constraints such as mode-transition duration, vehicle acceleration fluctuation and friction loss of the dry clutch. In addition, the engagement of dry clutch features torque discontinuity due to slip-stick phenomenon and the dynamic behavior of the ICE further increases the nonlinearity of the powertrain system.

Recent developments of hybrid vehicle technology have promoted another wave of vehicle electrification and introduction of pure electric vehicles (PEVs), such as Nissan Leaf and Ford Transit Connect Electric. The energy efficiency of these PEVs with an electric drive can be potentially further improved by introducing a two-speed or multi-speed gearbox to ensure the electric machine to operate at peak performance. In this work, a powertrain model of the Transit Connect Electric is built to examine the powertrain efficiency improvement potentials using a two-speed gearbox. The HEV and EV powertrain modeling tool, AUTONOMIE from US Argonne National Lab, is used for the powertrain modeling, and partially verified using vehicle testing data from US Environment Protection Agency (EPA). An optimization method, whose kernel is Dynamic Programming (DP), is combined with the model to find the possible minimum energy consumption and corresponding gear ratios.